using System;

namespace Org.BouncyCastle.Crypto.Tls
{
	/// <remarks>
	/// A queue for bytes.
	/// <p>
	/// This file could be more optimized.
	/// </p>
	/// </remarks>
	public class ByteQueue
	{
		/// <returns>The smallest number which can be written as 2^x which is bigger than i.</returns>
		public static int NextTwoPow(
			int i)
		{
			/*
			* This code is based of a lot of code I found on the Internet
			* which mostly referenced a book called "Hacking delight".
			*
			*/
			i |= (i >> 1);
			i |= (i >> 2);
			i |= (i >> 4);
			i |= (i >> 8);
			i |= (i >> 16);
			return i + 1;
		}

		/**
		 * The initial size for our buffer.
		 */
		private const int InitBufSize = 1024;

		/**
		 * The buffer where we store our data.
		 */
		private byte[] databuf = new byte[ByteQueue.InitBufSize];

		/**
		 * How many bytes at the beginning of the buffer are skipped.
		 */
		private int skipped = 0;

		/**
		 * How many bytes in the buffer are valid data.
		 */
		private int available = 0;

		/// <summary>Read data from the buffer.</summary>
		/// <param name="buf">The buffer where the read data will be copied to.</param>
		/// <param name="offset">How many bytes to skip at the beginning of buf.</param>
		/// <param name="len">How many bytes to read at all.</param>
		/// <param name="skip">How many bytes from our data to skip.</param>
		public void Read(
			byte[]	buf,
			int		offset,
			int		len,
			int		skip)
		{
			if ((available - skip) < len)
			{
				throw new TlsException("Not enough data to read");
			}
			if ((buf.Length - offset) < len)
			{
				throw new TlsException("Buffer size of " + buf.Length + " is too small for a read of " + len + " bytes");
			}
			Array.Copy(databuf, skipped + skip, buf, offset, len);
		}

		/// <summary>Add some data to our buffer.</summary>
		/// <param name="data">A byte-array to read data from.</param>
		/// <param name="offset">How many bytes to skip at the beginning of the array.</param>
		/// <param name="len">How many bytes to read from the array.</param>
		public void AddData(
			byte[]	data,
			int		offset,
			int		len)
		{
			if ((skipped + available + len) > databuf.Length)
			{
				byte[] tmp = new byte[ByteQueue.NextTwoPow(data.Length)];
				Array.Copy(databuf, skipped, tmp, 0, available);
				skipped = 0;
				databuf = tmp;
			}
			Array.Copy(data, offset, databuf, skipped + available, len);
			available += len;
		}

		/// <summary>Remove some bytes from our data from the beginning.</summary>
		/// <param name="i">How many bytes to remove.</param>
		public void RemoveData(
			int i)
		{
			if (i > available)
			{
				throw new TlsException("Cannot remove " + i + " bytes, only got " + available);
			}

			/*
			* Skip the data.
			*/
			available -= i;
			skipped += i;

			/*
			* If more than half of our data is skipped, we will move the data
			* in the buffer.
			*/
			if (skipped > (databuf.Length / 2))
			{
				Array.Copy(databuf, skipped, databuf, 0, available);
				skipped = 0;
			}
		}

		/// <summary>The number of bytes which are available in this buffer.</summary>
		public int Available
		{
			get { return available; }
		}
	}
}
